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HV857 Datasheet(PDF) 5 Page - Supertex, Inc |
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HV857 Datasheet(HTML) 5 Page - Supertex, Inc |
5 / 9 page 5 Supertex inc. www.supertex.com Doc.# DSFP-HV857 A062013 HV857 External Component Description External Component Description Diode Fast reverse recovery diode, BAS21 diode or equivalent. C S Capacitor 0.003µF to 0.1µF, 100V capacitor to GND is used to store the energy transferred from the inductor. R EL Resistor The EL lamp frequency is controlled via an external R EL resistor connected between REL-Osc and VDD of the device. The lamp frequency increases as R EL decreases. As the EL lamp frequency increases, the amount of current drawn from the battery will increase and the output voltage V CS will decrease. The color of the EL lamp is dependent upon its frequency. A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the R EL resistor by a factor of 2 will increase the lamp frequency by a factor of 2. f EL = (2MΩ)(240Hz) R EL R SW Resistor The switching frequency of the converter is controlled via an external resistor, RSW between RSW-Osc and VDD of the device. The switching frequency increases as R SW decreases. With a given inductor, as the switching frequency increases, the amount of current drawn from the battery will decrease and the output voltage, V CS, will also decrease. f SW = (560kΩ)(80Hz) R SW L X Inductor The inductor L X is used to boost the low input voltage by inductive flyback. When the internal switch is on, the inductor is being charged. When the internal switch is off, the charge stored in the inductor will be transferred to the high voltage capacitor C S. The energy stored in the capacitor is connected to the internal H-bridge, and therefore to the EL lamp. In general, smaller value inductors, which can handle more current, are more suitable to drive larger size lamps. As the inductor value decreases, the switch- ing frequency of the inductor (controlled by R SW) should be increased to avoid saturation. A 220µH Murata (LQH32CN221) inductor with 8.4Ω series DC resistance is typically recommended. For inductors with the same inductance value, but with lower series DC resistance, lower R SW resistor value is needed to prevent high current draw and inductor saturation. Lamp As the EL lamp size increases, more current will be drawn from the battery to maintain high voltage across the EL lamp. The input power, (V IN x IIN), will also increase. If the input power is greater than the power dissipation of the package, an external resistor in series with one side of the lamp is recom- mended to help reduce the package power dissipation. |
Similar Part No. - HV857_13 |
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Similar Description - HV857_13 |
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